Vascular disease is one of the leading causes of morbidity and mortality in the United States. For example, a common type of vascular disease is known as Atherosclerosis, a vascular disease that occurs in artery segments (for example, in the carotid artery, the renal arteries, and peripheral arteries of the limbs). Atherosclerosis (also known as hardening of the arteries) is a progressive, degenerative arterial disease that leads to occlusion of affected blood vessels, thereby reducing vessel patency, and hence, blood flow through the vessels. For example, plaques such as fatty substances, cholesterol, calcium and/or fibrin may build in the inner lining of arteries, thereby causing an occlusion that results in narrowing of the lumen of these blood vessels.
As arteries are internal, special procedures must be employed to locate the occlusion in the arteries. For example, a procedure known as catheterization is typically utilized in an attempt to locate a blocked blood vessel such as an artery. Differently shaped catheters may be introduced into the femoral artery, for example, by passing them through a sheath to locate the blocked artery, to measure the amount of oxygen in the blood, or to view blood flow, for example. Viewing blood flow is accomplished by a procedure known as angiography (also known as arteriography). The procedure involves injecting dye through a catheter while a series of rapid X-ray images is recorded. In this fashion, “movies” can be made to view blood flow.
Regardless, however, of the purpose for conducting a catherization procedure (for example, to determine the amount of oxygen in blood, to view blood flow, or to locate and unblock an artery), selection of the proper catheter size/dimension for a particular catherization procedure is a critical step. If a catheter having too large of a size (often referred to in French scale, 3F=1 mm) is inserted into a blood vessel, a variety of complications may occur. Complications include leakage around the catheter, encrustation, irritation, and infection. A serious type of complication can result from damage to the blood vessel and bleeding occasioned thereby. Extensive bleeding can lead to a host of various complications such as embolisms and aneurisms, etc., which can result in strokes or heart attacks. An oversized catheter may also perforate the wall of a proximate organ (for example, a kidney, in a renal catherization procedure). Further, sudden blockage of an artery may occur if the employed catheter is too large. This can also lead to a stroke, for example, and in some cases, utilizing a catheter of an inappropriate size may be fatal to a patient.
Thus, a significant amount of care must be taken to ensure that a properly sized catheter is selected for insertion into a particular vessel. Some medical professionals base catheter selection on guiding formulas developed by using attributes of patients such as height and age. These formulas, however, do not typically take into consideration the specifics of the particular patient being subjected to the intracorporeal surgical procedure. As a result, an incorrectly-sized catheter may be chosen.
In addition to using the above described attribute-based method for determining size of a vessel in an image, medical professionals attempt to determine vessel size by relying on experience to judge size of the vessel. This approach can lead to inaccurate determinations.
Another method for determining size of objects in images uses a “marker” catheter having a pair of radio-opaque markers spaced approximately two centimeters apart with a direct arithmetic proportional calculation based upon observed apparent lengths. This method, too, has disadvantages. First, it is often difficult to include both the markers and the anatomic region of interest on the same image during a procedure. Secondly, some conventional marker catheters do not have any mechanisms for ensuring that the line extending between the two markers is perpendicular to the image beam. This causes the image beam to foreshorten the apparent distance between the two markers on the image which can result in an inaccurate determination of the size of the anatomic structure in question. Thirdly, some conventional marker catheters are designed exclusively for intravascular use and ignore biliary and bronchial applications. Finally, a medical professional may begin a procedure with an unmarked catheter and may not realize until the procedure is already under way that it is desirable to measure the size of a structure. In such a case, it can be difficult, time-consuming, and expensive to exchange an unmarked catheter for a marked catheter.
A number of other methods have been developed in the prior art for determining the size of objects in images. For example, U.S. Pat. No. 2,819,526, issued to Brown, Jr., describes a calculator for use with X-ray images for determining object size in images. U.S. Pat. No. 4,974,164, issued to Lewis et al., describes a digital measuring and proportioning instrument comprising a hand-held microcomputer based ruler-like measuring and calculating instrument that is particularly adapted for measuring the sizes of objects in the field of graphic arts. In addition, U.S. Pat. No. 5,170,570, issued to Mays, Jr., describes a hand, finger, and joint measuring gauge for measuring objects. While the foregoing prior art devices and methods have proved useful, they suffer from a number of disadvantages. For instance, some are complex to use. Others are costly or have an inadequate measurement range.
Therefore, what is needed is an apparatus and method for assisting a medical professional with a more accurate selection of a properly sized catheter to be used in a vessel. Such an apparatus should allow a medical professional to more precisely measure the particular vessel at issue to determine a catheter size best fitted for the vessel.